Ultrasonographic elasticity imaging device

ABSTRACT

An ultrasonographic device includes an ultrasonic wave transmitter/receiver section which transmits and receives ultrasonic waves to and from a test subject through a probe, a phasing addition circuit which controls the phase of the received ultrasonic wave and generates RF signal frame data, an RF signal frame data selection section which makes variable the frame interval of the RF signal frame data to be outputted, and an elastic image generating section which sets the optimum imaging range for each elastic frame data generated based on the RF signal frame data and generates elastic image.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.10/542,206, filed Jul. 14, 2005, now U.S. Pat. No. 7,628,754, whichclaims priority from Japanese Patent Application No. JP 2003-006932,filed Jan. 15, 2003, the contents of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to an ultrasonographic device by which atomographic image of an examined part inside a test subject is obtainedand displayed using ultrasonic waves, and particularly relates to anultrasonographic device by which a distortion or an elastic modulus iscalculated for each point on an image based on a group of RF signalframe data arranged in time sequence, and is displayed as an elasticimage indicating the hardness or softness of living tissue in aquantitative manner.

BACKGROUND ART

A typical ultrasonographic device is conventionally constituted of anultrasonic wave transmitter/receiver section for transmitting andreceiving ultrasonic waves to and from a test subject, a tomographicscanning section for repeatedly obtaining tomographic image data in thetest subject including motor tissue in a predetermined cycle by using areflecting echo signal from the ultrasonic wave transmitter/receiversection, and an image display section for displaying time-sequencetomographic image data obtained by the tomographic scanning section.Further, the structure of living tissue in the test subject is displayedas, e.g., a B-mode image.

In relation to this device, in recent years, an external force isartificially applied from the body surface of the test subject through apressurizer or an ultrasound probe to measure a distortion and/orelastic modulus of living tissue of an examined part, and the hardnessof the tissue is displayed as an elastic image based on numeric data(elastic frame data) of a distortion or elastic modulus by using theultrasonographic device. Such an ultrasonographic device is disclosed inJP-A-5-317313 or JP-A-2000-60853.

However, in the imaging of elastic frame data in the ultrasonographicdevice of the citations, a correlation operation is used between two RFsignal frame data which are obtained in a series of pressuring ordecompressing operations and are adjacent to each other in timesequence. Thus, when an amount of pressurization or decompressionapplied in a time interval between RF signal frame data constituting agroup of two or more RF signal frame data does not sufficiently reach anamount of pressurization or decompression (generally about 1%) suitablefor visualizing elastic image data, it is difficult to properlyvisualize an elastic image of elastic frame data.

During a series of pressuring or decompressing operations, when anobject is diagonally and/or unevenly pressurized or decompressed, a timephase may occur in which a stress distribution in the object has atemporally irregular change. In such a time phase, a coordinate areawhere a stress distribution has a temporally irregular change appears ina series of elastic frame data (distortion data) in the time-basedirection. Thus, an elastic image includes a temporally irregular areaas noise, so that image diagnosis becomes difficult.

DISCLOSURE OF THE INVENTION

In consideration of the above-described point, it is an object of thepresent invention to provide an ultrasonographic device by which adifference in elasticity can be effectively visualized as an image witha high S/N ratio and a predetermined display gradation stably even in agiven time phase.

An ultrasonographic device of the present invention comprises:

an ultrasound probe including an oscillator for generating ultrasonicwaves, an ultrasonic wave transmitter/receiver circuit which isconnected to the probe and transmits and receives the ultrasonic wavesto and from a test subject, a phasing addition circuit which controlsthe phase of received ultrasonic waves and generates RF signal framedata, an RF signal frame data selection section which is connected tothe phasing addition circuit and makes variable a frame interval ofoutputted RF signal frame data according to a change in pressure appliedto the test subject, an elastic frame data calculation section which isconnected to the RF signal frame data selection section and generateselastic frame data in time sequence based on a pair of the inputted RFsignal frame data, the elastic frame data indicating a distortion or anelastic modulus of each point on a tomographic image, and an elasticimage generating section which is connected to the elastic frame datacalculation section and generates an elastic image based on the elasticframe data inputted from the calculation section.

Further, in the ultrasonographic device of the present invention, theelastic image generating section includes a statistical processingcircuit for performing statistical processing on two or more elasticframe data corresponding to a target processing area and determines astatistical characteristic amount, a circuit for setting the upper limitvalue and the lower limit value of an imaging range of the elastic framedata based on the statistical characteristic amount, and a circuit forgenerating elastic image data from the elastic frame data while matchingthe upper limit value and the lower limit value with the range of apredetermined display gradation.

Other objects, features, and advantages of the present invention willbecome apparent from the following description of examples withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of an ultrasonographicdevice according to the present invention;

FIG. 2 is a diagram showing an example of an RF signal frame dataselection section shown in FIG. 1;

FIG. 3 is a diagram showing another example of the RF signal frame dataselection section shown in FIG. 1;

FIG. 4 is a diagram showing an example of a method of measuring apressure between the head of an ultrasound probe and a test subject bymeans of a pressure measurement section (pressure sensor) attached tothe probe;

FIG. 5 is a diagram showing an example of the operations of an elasticdata processing section shown in FIG. 1;

FIG. 6 is a diagram showing another example of the operations of theelastic data processing section shown in FIG. 1;

FIG. 7 is a diagram showing a relationship before and after logarithmictransformation on elastic frame data in the elastic data processingsection;

FIG. 8 is a diagram showing an example in which two or more functionsare combined to transform elastic frame data in the elastic dataprocessing section;

FIG. 9 is a diagram showing another example of the operations of theelastic data processing section shown in FIG. 1;

FIG. 10 is a diagram showing an example of the relationship between atemporal change in pressurization/decompression speed and the timing forobtaining an RF signal;

FIGS. 11A and 11B are diagrams showing a temporal change of an elasticimage luminance distribution when the upper limit value and the lowerlimit value of elastic frame data are set in a fixed manner;

FIGS. 12A and 12B are diagrams showing a temporal change of the elasticimage luminance distribution when the upper limit value and the lowerlimit value of the elastic frame data are properly set understatistically shared conditions in the elastic data processing sectionof FIG. 9; and

FIG. 13 is a diagram showing an example of the cooperative operations ofthe RF signal frame data selection section and the elastic dataprocessing section.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will specifically describe an embodiment of the presentinvention in accordance with the accompanying drawings. FIG. 1 is ablock diagram showing an embodiment of an ultrasonographic device of thepresent invention. With the ultrasonographic device, a tomographic imageof an examined part of a test subject 100 is obtained using ultrasonicwaves, and an elastic image indicating the hardness or softness ofliving tissue can be displayed. As shown in FIG. 1, the ultrasonographicdevice comprises an ultrasound probe 101, a radio transmitter circuit102, a receiver circuit 103, a phasing addition circuit 104, a signalprocessing section 105, a monochrome scan converter 106, an imagedisplay device 107, an RF signal frame data selection section 108, adisplacement measurement section 109, a pressure measurement section110, a distortion/elastic modulus calculation section 111, an elasticdata processing section 112, a color scan converter 113, and achange-over adder 114.

The ultrasound probe 101, the radio transmitter circuit 102, thereceiver circuit 103, the phasing addition circuit 104, and the signalprocessing section 105 constitute an ultrasonic wavetransmitter/receiver section. The ultrasonic wave transmitter/receiversection causes an ultrasonic beam to scan the inside of the body of atest subject by using the ultrasound probe 101 along a fixed direction,so that a tomographic image is obtained. The ultrasound probe 101 isformed of a number of oscillators arranged like strips. The ultrasoundprobe 101 performs beam scanning mechanically or electronically totransmit and receive ultrasonic waves to and from a test subject. Theultrasound probe 101 includes oscillators (not shown) where ultrasonicwaves are generated and reflecting echo is received. The oscillators aregenerally formed with the function of converting an inputted pulse waveor a transmission signal of a continuous wave into an ultrasonic waveand emitting the ultrasonic wave, and the function of receiving anultrasonic wave reflected from the inside of the test subject,converting the ultrasonic wave into a reception signal of an electricsignal, and outputting the signal.

The radio transmitter circuit 102 generates a transmission pulse fordriving the ultrasound probe 101 and generating ultrasonic waves, andsets the convergent point of a transmitted ultrasonic wave at a certaindepth by means of a transmission phasing addition circuit included inthe radio transmitter circuit 102. The receiver circuit 103 amplifies areflecting echo signal, which has been received by the ultrasound probe101, with a predetermined gain. Amplified reception signals as many asthe oscillators are inputted as independent reception signals to thephasing addition circuit 104. The phasing addition circuit 104 is fedwith the reception signals having been amplified by the receiver circuit103, controls the phases of the signals, and forms ultrasonic beams forone or more convergent points. The signal processing section 105 is fedwith the reception signals from the phasing addition circuit 104 andperforms various kinds of signal processing such as gain correction, logcompression, detection, edge enhancement, and filter processing.

The monochrome scan converter 106 obtains RF signal frame data in thetest subject 100 including motor tissue in an ultrasonic cycle by usinga reflecting echo signal outputted from the signal processing section105 of the ultrasonic wave transmitter/receiver section, and themonochrome scan converter 106 displays the RF signal frame data on theimage display device 107 via the change-over adder 114. One RF signalframe data constitutes an image. Therefore, the monochrome scanconverter 106 includes a tomographic scanning section for sequentiallyreading RF signal frame data in a cycle of television system and variouscontrol circuits for controlling a system. For example, the monochromescan converter 106 includes an A/D converter for converting thereflecting echo signal from the signal processing section 105 into adigital signal, a plurality of frame memories for storing tomographicimage data, which has been digitized by the A/D converter, in timesequence, and a controller for controlling these operations.

The image display device 107 displays the time-sequence tomographicimage data having been obtained by the monochrome scan converter 106.The image display device 107 is constituted of a D/A converter forconverting image data, which is outputted from the monochrome scanconverter 106 via the change-over adder 114, into an analog signal, anda color television monitor which is fed with an analog video signal fromthe D/A converter and displays the signal as an image.

In this embodiment, the RF signal frame data selection section 108 andthe displacement measurement section 109 are disposed so as to branchoff from the output side of the phasing addition circuit 104, and thepressure measurement section 110 is provided in parallel with the RFsignal frame data selection section 108 and the displacement measurementsection 109. The distortion/elastic modulus calculation section 111, theelastic data processing section 112, and the color scan converter 113are provided in the subsequent stages of the displacement measurementsection 109 and the pressure measurement section 110. The change-overadder 114 is provided on the output side of the color scan converter 113and the monochrome scan converter 106.

Referring to FIG. 2, the operations of the RF signal frame dataselection section 108 will be discussed below according to the presentembodiment. FIG. 2 is a diagram showing an example of the RF signalframe data selection section of FIG. 1. The RF signal frame dataselection section 108 arbitrarily selects the number of past frames (thenumber of frame intervals from the current frame data) as one RF signalframe data serving as the reference of displacement measurement. Inother words, the RF signal frame data selection section 108 sequentiallyobtains RF signal frame data, which is successively outputted from thephasing addition circuit 104 in time sequence at the frame rate of theultrasonographic device, in a frame memory 1081. The RF signal framedata selection section 108 sets the latest data, which is currentlyobtained in the frame memory 1081, as RF signal frame data Q. The RFsignal frame data selection section 108 selects one of the past RFsignal frame data Q-1, Q-2, Q-3, . . . , and Q-M in response to acontrol command from a control section 200 of the ultrasonographicdevice, and temporarily stores the data as RF signal frame data R in anRF signal frame data selection circuit 1082. The RF signal frame dataselection section 108 outputs in parallel the latest RF signal framedata Q stored in the frame memory 1081 and the RF signal frame data Rstored in the RF signal frame data selection circuit 1082 to thedisplacement measurement section 109.

In other words, first, the RF signal frame data selection section 108can arbitrarily select not only the RF signal frame data Q-1, whichtemporally adjoins to the current RF signal frame data Q, but also theRF signal frame data Q-M, which is obtained by thinning out M frames(M=1, 2, 3, . . . ), as the past RF signal frame data R constituting agroup of RF signal frame data to be sent to the displacement measurementsection 109. Besides, M frame intervals (M=1, 2, 3, . . . ) can bearbitrarily set and changed by the user interface of theultrasonographic device when a change in pressure applied to an examineethrough the ultrasonic wave transmitter/receiver section cannot besufficiently large.

FIG. 3 is a diagram showing another example of the RF signal frame dataselection section of FIG. 1. The RF signal frame data selection section108 of FIG. 3 obtains RF signal frame data P, which has been obtained ina certain time phase P of the past, in the frame memory 1081 in responseto a control command from the control section 200 of theultrasonographic device. The RF signal frame data selection circuit 1082always refers to the RF signal frame data P, which is obtained in theframe memory 1081, as past RF signal frame data in a given time phasewithout updating. Therefore, the displacement measurement section 109obtains a group of RF signal frame data constituted of the currentlyobtained RF signal frame data Q and the RF signal frame data P.Regarding whether to use the function of FIG. 3 or the setting of thetiming for obtaining the RF signal frame data P when the function isused, it is possible to freely make a switching, setting, and change bythe user interface of the ultrasonographic device when a change inpressure applied to the examinee through the ultrasonic transmit/receivesection cannot be increased sufficiently.

When an interval between past and current RF signal frame dataconstituting a group of RF signal frame data is limited to adjacentframes, an amount of pressurization or decompression applied in a timeinterval between the RF signal frame data may not sufficiently reach anamount of pressurization or decompression (generally about 1%) suitablefor visualizing elastic image data. The RF signal frame data constitutesa group of two or more RF signal frame data having been obtained duringa series of pressurizing or decompressing operations. In contrast, withthe RF signal frame data selection section shown in FIGS. 2 and 3, it ispossible to sufficiently increase a frame interval between past andcurrent RF signal frame data, thereby properly visualizing an elasticimage of elastic frame data. The RF signal frame data selection sectionis particularly useful in a state in which a pressuring or decompressingspeed cannot be sufficiently increased in a series of pressurizing ordecompressing operations in ultrasonography due to a physicalrestriction of the build of the examinee. The frame interval can bearbitrarily set and changed after the user confirms a change of anelastic image.

The displacement measurement section 109 performs a one-dimensional ortwo-dimensional correlation operation based on the group of RF signalframe data having been selected by the RF signal frame data selectionsection 108, and measures a displacement or a mobile vector (thedirection and amount of a displacement) of each point on a tomographicimage. A method of detecting the mobile vector includes, e.g., a blockmatching method and a gradient method which are described inJP-A-5-317313. In the block matching method, an image is divided into,e.g., blocks of N×N pixels, the previous frame is searched for a blockthe most analogous to a noticed block in the current frame, andpredictive coding is performed with reference to the block.

Also, a displacement or a mobile vector of each point on a tomographicimage can be determined based on an amount of movement of the probe froma surface of the test subject.

The amount of movement of the probe can be determined using atransmitter and a receiver, each of which has a unique coordinate spaceof a three-axis orthogonal system as disclosed in JP-A-10-151131. Whenthe receiver is disposed in the probe and the transmitter is disposednear the test subject so as not to move, it is possible to locate thereceiver in the coordinate space set by the transmitter. With thisconfiguration, it is possible to obtain the amount of movement of theprobe which moves with a pressure applied to the test subject. Forexample, the transmitter can be composed of a magnetic field generatingcoil for generating a magnetic field of the three-axis orthogonalsystem, and the receiver can be composed of a detection coil capable ofdetecting a magnetic field of the three-axis orthogonal system. Thetransmitter and the receiver are disposed such that the coil surfaces ofthe magnetic field generating coil and the magnetic field detection coilof the three-axis orthogonal system are orthogonal to each other.Alternating current is applied to each coil of the transmitter togenerate an alternating magnetic field. The generated alternatingmagnetic field is detected by the detection coil of the receiver. Eachdirectional component of the detected magnetic field and the intensityof the magnetic field are calculated by an arithmetic unit (not shown),so that the positional relationship between the transmitter and thereceiver can be recognized. The amount of movement of the probe iscalculated based on the calculated positional relationship and isreflected on RF frame data to obtain elastic frame data. Alternatively,elastic frame data is obtained from the calculated amount of movement.

The pressure measurement section 110 measures or estimates the in vivopressure of an examined part of the test subject 100. In theultrasonographic device, the following method is used: while ultrasonicwaves are transmitted and received under the control of the controlsection 200 by using the ultrasound probe 101 disposed on the probe head1011, a pressure is increased or reduced by using a pressurizer 115disposed on a probe head 1011, so that a stress distribution is providedin the body cavity of the examined part of the test subject 100. In thismethod, in order to measure a pressure applied between the probe head1011 and the test subject 100, a pressure sensor 1012 for detecting apressure applied to a rod-like member is attached to, e.g., the side ofthe probe head 1011 as shown in FIG. 4, a pressure between the probehead 1011 and the test subject 100 is measured in a given time phase,and a measured pressure value is transmitted to the distortion/elasticmodulus calculation section 111. In FIG. 4, the pressurizer 115 may beprovided which is attached to the probe head 1011 and automaticallypressurizes or decompresses a living body.

The distortion/elastic modulus calculation section 111 calculates adistortion and an elastic modulus of each point on a tomographic imagebased on an amount of movement (displacement ΔL) and a change inpressure (ΔP) which are outputted from the displacement measurementsection 109 and the pressure measurement section 110, respectively, togenerate numeric data of a distortion and an elastic modulus (elasticframe data), and outputs the data to the elastic data processing section112. When a distortion is calculated by the distortion/elastic moduluscalculation section 111, the distortion may be calculated by, e.g., aspace differentiation (ΔL/ΔX) performed on the displacement ΔL withoutusing pressure data. ΔX represents a displacement of a coordinate. AYoung's modulus Ym, which is one of elastic moduli, may be calculated bythe following equation in which a change in pressure is divided by achange in the amount of movement:Ym=(ΔP)/(ΔL/L)where L represents the original length.

FIG. 5 is a diagram showing an example of the operations of the elasticdata processing section shown in FIG. 1. The elastic data processingsection 112 sequentially obtains elastic frame data X, which issuccessively inputted from the distortion/elastic modulus calculationsection 111 in time sequence, in a frame memory 1121. The elastic dataprocessing section 112 sets, as elastic frame data N, elastic frame datacurrently obtained in the frame memory 1121. Therefore, elastic framedata N, N-1, N-2, . . . , N-M are stored in this order in the framememory 1121 in time sequence. In response to a control command from thecontrol section 200 of the ultrasonographic device, anaddition/averaging circuit 1122 selects elastic frame data of M framesin turn, starting from the most analogous data at the present time, outof the elastic frame data having been obtained in the frame memory 1121.The addition/averaging circuit 1122 performs addition and averaging onthe same coordinate data point based on the current elastic frame dataN, which has been selected from the frame memory 1121, and the pastelastic frame data N-1, N-2, . . . N-M of M frames. The elastic framedata obtained by the addition and averaging is transmitted as currentelastic frame data Y to the color scan converter 113. Regarding thenumber M of past elastic frame data selected by the addition andaveraging on elastic frame data and a decision on whether to use thefunction of addition and averaging on elastic frame data, it is possibleto freely make a setting and change in the user interface of theultrasonographic device.

The above operations are expressed by the following equation:

(elastic  frame  data  Y) i, j = {(elastic  frame  data  N) i, j + (elastic  frame  data  N-1) i, j + (elastic  frame  data  N-2)i, j + … + (elastic  frame  data  N-M) i, j} ÷ (M + 1)where indexes i and j represent the coordinates of each frame data.

The addition/averaging circuit 1122 in the elastic data processingsection of the present embodiment performs addition and averaging onelastic frame data in the time-base direction. Thus, it is possible tosmooth a temporally irregular area of a stress distribution in an objectinto a continuous area, thereby reducing noise. The irregular areaoccurs when the object is unevenly pressurized or decompressed in adiagonal direction.

FIG. 6 is a diagram showing another example of the operations of theelastic data processing section shown in FIG. 1. The elastic dataprocessing section 112 of this example performs logarithmictransformation on inputted elastic frame data. The elastic dataprocessing section 112 obtains elastic frame data X, which issuccessively outputted from the distortion/elastic modulus calculationsection 111 in time sequence, in a frame memory 1123, causes acompression circuit 1124 to perform logarithmic transformation on thedata according to a correspondence between elastic image data andelastic frame data reflecting an instruction of a control command fromthe control section 200 of the ultrasonographic device, and transmitsthe transformed elastic frame data as elastic frame data Y to the colorscan converter 113. When inputted elastic frame data is expressed by[(elastic frame data X) i,j] and outputted elastic frame data isexpressed by [(elastic frame data Y) i,j], a logarithm operationperformed by the elastic data processing section 112 of FIG. 6 isexpressed by the following equation:(elastic frame data Y)i,j=A×Log10[B×{(elastic frame data X)i,j+C}+1]where indexes i and j represent the coordinates of each frame data, andA, B, and C represent certain constants. Particularly regarding thecombination of the constants A, B, and C in the above equation and adecision whether to use the compressing function, it is possible tofreely make a setting and change in the user interface of theultrasonographic device.

Particularly in image diagnosis using elastic images, it is highlysignificant to clearly detect a hard portion suspected of being a cancertissue. Thus, it is important to clearly visualize a hard area. There isa report describing a property of a living tissue (T. A. Krouskop et al,Ultrasonic Imaging, 1998). According to this report, an adipose tissueand a cancer tissue are different in hardness by several tens times in,e.g., a mammy gland area. However, regarding the elastic imaging ofelastic frame data in hue information converting means for color displayor monochrome luminance information converting means for monochromedisplay in the existing ultrasonographic device, the values of elasticframe data and the values of elastic image data have a linearrelationship as indicated by a broken line of FIG. 7. Thus, in the casewhere a difference in the hardness of tissue is visualized in the sameelastic image, in any area selected as an imaging range in elastic framedata, the process of a spatial change in hardness between two areas of asoft area and a hard area can be expressed only by a linearrelationship, so that it is difficult to clarify the hard area andrecognize the edge of a hardened portion. In other words, only two areasof an extremely soft area and an extremely hard area are clearlyvisualized like a binarized image, and thus it has been difficult toproperly express a large change in hardness from the soft area to thehard area as hue information or monochrome luminance information.Therefore, in some cases, it is difficult to determine the size of ahardened cancer tissue in elastic image diagnosis. In contrast,according to the above-described embodiment in which the compressioncircuit 1124 is used in the elastic data processing section 112, asindicated by a solid line of FIG. 7, an area having small values (hardarea) becomes elastic frame data of values sharply changing in acoordinate space and an area having large values (soft area) becomeselastic frame data of values gradually changing in the coordinate spacein inputted elastic frame data. When elastic image data is generatedbased on elastic frame data outputted from the elastic data processingsection 112, it is possible to clearly display a hard area, therebyrecognizing the edge of a hardened portion.

Logarithmic transformation was described as an example of dataconversion performed by the compression circuit 1124 of the elastic dataprocessing section 112 shown in FIG. 6. Compression may be performedusing another transfer function having a property enabling theabove-described object. For example, Y=A×(1−Exp (−B×X)) or the like maybe used where A and B represent constants. Further, several kinds oftransfer functions may be prepared and freely set and changed by theuser interface of the ultrasonographic device. Moreover, one transferfunction may be composed of, e.g., two or more curves as shown in FIG.8. In the function of FIG. 8, an intersection point G may be freely setand changed vertically and horizontally. Hence, it is possible to freelyset the sensitivity of a hard portion and a soft portion.

FIG. 9 is a diagram showing still another example of the operations ofthe elastic data processing section 112 shown in FIG. 1. The elasticdata processing section 112 of FIG. 9 performs statistical processing oninputted elastic frame data. Specifically, the elastic data processingsection 112 of FIG. 9 obtains elastic frame data X, which issuccessively outputted from the distortion/elastic modulus calculationsection 111 in time sequence, in the frame memory 1123 of the elasticdata processing section 112. In a coordinate area of elastic frame datareflecting an instruction of a control command (statistic processingarea information 1126) from the control section 200 of theultrasonographic device, a statistical processing circuit 1125 of theelastic data processing section 112 performs statistical processing onthe elastic frame data. The statistical processing circuit 1125determines, based on a statistical characteristic amount obtained as aresult, the upper limit value and the lower limit value of the elasticframe data selected as the range of image data when elastic image datais generated, and transmits elastic frame data Y and the upper and lowerlimit values to the color scan converter 113. The elastic frame data Ymay be given elastic frame data X or an average value of a processingarea.

As a statistical characteristic amount in the statistical processingcircuit 1125 of FIG. 9, for example, an average value and a variancevalue may be obtained. The average value and the variance value areexpressed by the following equation:

$\begin{matrix}{\left( {{average}\mspace{14mu}{value}} \right) = {\left\lbrack {{\sum{\left( {{elastic}\mspace{14mu}{frame}\mspace{14mu}{data}\mspace{14mu} X} \right)\; i}},j} \right\rbrack \div}} \\{\left( {{the}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{processing}\mspace{14mu}{area}\mspace{14mu}{data}} \right)} \\{\left( {{variance}\mspace{14mu}{value}} \right)^{2}} \\{= \left\lbrack {\sum\left\{ {{\left( {{elastic}\mspace{14mu}{frame}\mspace{14mu}{data}\mspace{14mu} X} \right)\; i},{j -}} \right.} \right.} \\{\left. \left. \left( {{average}\mspace{14mu}{value}} \right) \right\}^{2} \right\rbrack \div} \\{\left( {{the}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{processing}\mspace{14mu}{area}\mspace{14mu}{data}} \right)}\end{matrix}$where [(elastic frame data X) i,j] represents inputted elastic framedata. In this equation, Σ represents a sum of data elements in thecoordinate area of elastic frame data reflecting the statisticalprocessing area information 1126, which is a control command from thecontrol section 200 of the ultrasonographic device.

As the upper limit value and the lower limit value of elastic frame dataselected as a range of image data during the generation of elastic imagedata, the following may be obtained:(upper limit value)=(average value)+(constant D)×(variance value){or(upper limit value)=(constant D′)×(average value)}(lower limit value)=(average value)−(constant E)×(variance value){or(lower limit value)=(constant E′)×(average value)}

The obtained upper limit value and lower limit value may be transmittedto the color scan converter 113. The constant D or D′ and the constant Eor E′ may be freely set and changed in the user interface of theultrasonographic device. Further, one of the upper limit value and thelower limit value may be set by the above equations and the other may beset at a fixed value not reflecting the statistical characteristic ofelastic frame data. For example, the lower limit value may be fixed at adistortion amount of 0% and the upper limit value may be set to averagevalue+2×variance value.

FIG. 10 is a diagram showing an example of the relationship between atemporal change in pressurization/decompression speed and the timing forobtaining an RF signal. As is evident from FIG. 10, when apressurization or decompression speed V varies during a series ofpressurizing or decompressing operations, the same coordinate region ofelastic frame data E1 to E4 has a statistical distribution (histogram)schematically shown based on the same scale in FIGS. 11A and 11B.Elastic frame data calculated by a pair of RF signal frame data S1 andRF signal frame data S2 is represented as E1, elastic frame datacalculated by a pair of RF signal frame data S2 and RF signal frame dataS3 is represented as E2, elastic frame data calculated by a pair of RFsignal frame data S3 and RF signal frame data S4 is represented as E3,and elastic frame data calculated by a pair of RF signal frame data S4and RF signal frame data S5 is represented as E4. The vertical axisrepresents the number of data elements and the horizontal axisrepresents a distortion amount.

As shown in FIG. 11A, in a series of elastic frame data having beenobtained in time series, the elastic frame data E1 to E4 of the samearea changes over time. In other words, when a pressurization ordecompression speed varies during a series of pressurizing ordecompressing operations, elastic frame data of the same area variesaccording to a change in pressurization or decompression speed, in theseries of elastic frame data having been obtained in time sequence. Inthe elastic imaging of elastic frame data in the hue informationconverting means and the monochrome luminance information convertingmeans of the conventional ultrasonographic device, the values of elasticframe data and the values of elastic image data are fixed in aone-to-one correspondence. For example, elastic image data EP1 to EP4are generated while the upper limit value and the lower limit valueobtained by optimization using the elastic frame data E2 of FIGS. 11Aand 11B are used as the upper limit value and the lower limit value ofthe elastic frame data E1 to E4 in a given time phase. In this case, inthe time phase of the elastic frame data E3, the elastic image data EP3is obtained by which an area calculated with a relatively largedistortion is not imaged. Conversely, in the time phase of the elasticframe data E1, the elastic image data EP1 is obtained by which an areacalculated with a relatively small distortion is not imaged. Unlike atime phase when the elastic frame data E2 is obtained, elastic imagedata like the elastic image data EP2 of optimized gradation cannot bealways generated in a given time phase.

In this way, in the elastic imaging of elastic frame data in the colorscan converter of the conventional ultrasonographic device, when apressurization or decompression speed varies, an image (FIG. 11B) isobtained which varies in monochrome luminance or hue in the same area ofa series of elastic image data having been obtained in time sequence, sothat image diagnosis becomes difficult. In other words, in all timephases, the fixed correspondence does not always optimize the contrastof an elastic image. In contrast, when the pressurization ordecompression speed V varies during a series of pressurizing ordecompressing operations as shown in FIG. 10, the statistical processingcircuit of the elastic data processing section of FIG. 9 performsstatistical processing on elastic frame data in a given time phase, andsets the upper limit value and the lower limit value of an imaging rangeaccording to the statistical characteristic amount. For example,(average value)±(constant D)×(variance value) shown in FIG. 12A iscalculated as an imaging range for the elastic frame data of a giventime phase. In this case, the constant D is a shared value in the giventime phase. Thus, the optimum imaging range is set for each of theelastic frame data.

The statistically shared upper and lower limit values having beenobtained thus for elastic frame data in a given time phase aretransmitted to the color scan converter, and elastic image data isgenerated within the range from the upper limit value to the lower limitvalue, so that elastic image data EP11 to EP14 can be generated with theefficient gradation of elastic frame data elements in a given time phaseas shown in FIG. 12B. With the statistical processing circuit in theelastic data processing section of the present embodiment, even when apressurization or decompression speed varies, it is possible to reduce achange in the monochrome luminance or hue of the same area in a seriesof elastic image data having been obtained in time sequence, and providean image with predetermined display gradation which is temporallystable, thereby facilitating image diagnosis. In other words, a ratio ofthe number of pixels exceeding the upper limit value of displaygradation in elastic image data and a ratio of the number of pixelsfalling below the lower limit value can be standardized to a fixeddistribution curve in a given time phase, and an image can be obtainedwith a smaller change in monochrome luminance or hue.

In FIGS. 12A and 12B, elastic image data is generated such that anaverage value of the distortions of elastic frame data matches with thecenter of a predetermined display gradation range.

The foregoing embodiment described, as one of the operations of the RFsignal frame data selection section, the case where a pair of RF signalframe data is selected and the number of frame intervals between thepair of RF signal frame data is made variable. Further, the foregoingembodiment described, as an example of an operation in the elastic dataprocessing section, the case where statistical processing is performedon elastic frame data in the statistical processing circuit provided inthe elastic data processing section. The following will describe thecase where the RF signal frame data selection section and the elasticdata processing section operate in cooperation with each other.

FIG. 13 is a diagram showing an example of the cooperative operation ofthe RF signal frame data selection section and the elastic dataprocessing section. First in the RF signal frame data selection section108, information (current frame interval number information 131) on thenumber of frame intervals between a pair of RF signal frame data usedfor generating current elastic frame data is transmitted to a frameinterval optimization circuit 1127 of the elastic data processingsection 112. Further, the statistical processing circuit 1125 of theelastic data processing section 112 performs statistical processing oncurrent elastic frame data and transmits information on a statisticalcharacteristic amount as a processing result to the frame intervaloptimization circuit 1127. Based on the current frame interval numberinformation 131 outputted from the RF signal frame data selectioncircuit 1082 and the information on the statistical characteristicamount of the current elastic frame data from the statistical processingcircuit 1125, the frame interval optimization circuit 1127 calculatesthe optimum number of frame intervals between a pair of RF signal framedata used for generating the subsequent elastic frame data, and feedsback information on the optimum number of frame intervals as subsequentframe interval number information 132 to the RF signal frame dataselection circuit 1082. The RF signal frame data selection circuit 1082sets the number of frame intervals between the pair of RF signal framedata used for generating the subsequent elastic frame data, based on theoptimum number of frame intervals (subsequent frame interval numberinformation 132), the optimum number being outputted from the frameinterval optimization circuit 1127.

The following will describe an example of the operations of the frameinterval optimization circuit 1127. The number of frame intervals (thecurrent number of frame intervals) of a pair of RF signal frame data forgenerating current elastic frame data and an average value of distortionamounts as a statistical processing result of the current elastic framedata are inputted to the frame interval optimization circuit 1127. Whena constant H is set to 0.5 to 2.5, the optimum number of frame intervalsis determined by the equation below:(the optimum number of frame intervals)=(constant H)×(the current numberof frame intervals)÷(average value of distortion amounts)The closest natural number to the optimum number of frame intervalsobtained thus is transmitted to the RF signal frame data selectioncircuit 1082 as information (subsequent frame interval numberinformation 132) on the number of frame intervals of a pair of RF signalframe data for generating the subsequent elastic frame data. Forexample, when the constant H is set to “1”, the number of frameintervals expected to have a distortion amount of about 1% in thesubsequent elastic frame data is transmitted to the RF signal frameselection section.

In image diagnosis using an elastic image, the contrast resolution of ahard area and a soft area considerably depends on a pressurization ordecompression amount which is physically applied in a time intervalduring which a pair of RF signal frame data is obtained. Generally, itis said that an elastic image having the highest contrast resolution isconsequently obtained in the range of pressurization or decompressionamounts enabling a distortion amount of about 0.5 to 2.5%. As describedin the embodiment shown in FIG. 13, when the RF signal frame dataselection section 108 and the frame interval optimization circuit 1127of the elastic data processing section 112 are configured in acooperative manner, even in a process where a large or small pressure isadded or reduced so instantly as to considerably deviate from theoptimum range of distortion amounts as an elastic image, such a state isinstantly handled by optimizing the number of frame intervals between apair of RF signal frame data, thereby visualizing a temporally stableelastic image with high contrast resolution.

The color scan converter 113 comprises a hue information conversionsection which is fed with elastic frame data outputted from the elasticdata processing section 112 and a command outputted from the controlsection 200 of the ultrasonographic device or the upper and lower limitvalues for determining a gradation selection range in elastic frame dataoutputted from the elastic data processing section 112, and which addshue information of red, green, blue and the like when elastic image datais generated from the elastic frame data. For example, in elastic framedata outputted from the elastic data processing section 112, the hueinformation conversion section operates so as to convert an area havinga large measured distortion into a red code in the elastic image dataand conversely converts an area having a small measured distortion intoa blue code in the elastic image data. The color scan converter 113 maybe constituted of the monochrome scan converter 106. In this case, thearea having a large measured distortion is increased in luminance in theelastic image data and conversely the area having the small measureddistortion is reduced in luminance in the elastic image data. Theelastic image data may be generated using the RF signal frame dataselection section 108 of FIGS. 2 and 3, the color scan converter 113,and the elastic data processing section constituted of a combination oftwo or more elastic data processing sections operating in differentmanners as shown in FIG. 5, 6, 9, or 13.

Further, the change-over adder 114 is means which is fed with monochrometomographic image data from the monochrome scan converter 106 and colorelastic image data from the color scan converter 113 and adds orswitches images. Switching is made such that only monochrome tomographicimage data or color elastic image data is outputted or both image datais outputted after addition. For example, as described inJP-A-2000-60853, a monochrome tomographic image and a color elasticimage or a monochrome elastic image obtained by the monochrome scanconverter may be simultaneously displayed on dual display. Image dataoutputted from the change-over adder 114 is outputted to the imagedisplay device 107.

As another display example of an image, a monochrome tomographic imageand a monochrome elastic image may be transmitted to the image displaydevice 107 without addition to display a monochrome tomographic imageand a color elastic image on one display screen in an overlappingmanner. Alternatively, two screens of a monochrome tomographic image anda monochrome elastic image may be simultaneously displayed on the samescreen. The monochrome tomographic image is not particularly limited toan ordinary B image. A tissue harmonic tomographic image may be usedwhich is an image generated by selecting the harmonic content of areception signal. Similarly a tissue Doppler image may be displayedinstead of the monochrome tomographic image. Additionally, images to bedisplayed on dual screens may be selected from various combinations.

Regarding the formation of the elastic image, the above explanationdescribed the case where elastic image data is generated after adistortion or a Young's modulus Ym of living tissue is obtained. Thepresent invention is not limited to this case. For example, an elasticmodulus may be calculated using other parameters such as a stiffnessparameter β, a pressure elastic modulus Ep, and an incremental elasticmodulus Einc (see JP-A-5-317313).

The embodiment shown in FIG. 1 described the case where an ultrasoundprobe is brought into contact with the body surface of a test subject.The present invention is not limited to this case. A transoesophagealprobe or an intravascular probe may be similarly used. According to thisembodiment, it is possible to achieve high reliability and stability inthe ultrasonographic device.

According to this invention, it is possible to stably visualize anelastic image with a high resolution at a given time and simultaneouslyachieve means for visualizing, as an image sequence, the response ofpalpation conventionally conducted by the doctor, thereby providing anultrasonographic device which is clinically useful while keeping thereal-time performance and convenience of ultrasonography.

Having described examples of the present invention. It will be obviousto those skilled in the art that the present invention is not limited tothese examples and various modifications and variations are possiblewithin the spirit of the present invention and the scope of the appendedclaims.

1. An ultrasonographic device, comprising: an ultrasound probe including an oscillator configured to generate an ultrasonic wave; an ultrasonic wave transmitter/receiver section which is connected to the probe and configured to transmit and receive the ultrasonic wave to and from a test subject; an elastic frame data calculation section configured to generate elastic frame data from the received ultrasonic wave; a processing section configured to set an upper limit value and a lower limit value of a gradation range for imaging so that a statistical characteristic amount of said elastic frame data generated by said elastic frame data calculation section matches with a center of the gradation range; and an elastic image generating section configured to generate an elastic image based on said elastic frame data by correlating the gradation range to said upper limit value and said lower limit value.
 2. The ultrasonographic device according to claim 1, wherein said statistical characteristic amount is an average value and a variance value of said elastic frame data.
 3. The ultrasonographic device according to claim 1, wherein said processing section is configured to obtain said upper and lower limit values by the following equations: upper limit value=(average value)+(constant D)×(variance value); and lower limit value=(average value)−(constant E)×(variance value).
 4. The ultrasonographic device according to claim 3, wherein said constant can be changed.
 5. The ultrasonographic device according to claim 3, wherein said constant is a shared value in a give time phase.
 6. The ultrasonographic device according to claim 1, wherein an average value of distortion matches with the center of the gradation range.
 7. The ultrasonographic device according to claim 1, wherein said elastic image generating section is configured to include: means for obtaining an average value and a variance value of the two or more elastic frame data, and determining at least one of the upper limit value and the lower limit value based on the average value and the variance value.
 8. The ultrasonographic device according to claim 1, further comprising: a phasing addition section configured to control a phase of the received ultrasonic wave and to generate RF signal frame data; an RF signal frame data selection section configured to select said RF signal frame data; wherein said elastic image generating section is configured to include frame interval optimization means which receives, from said RF signal frame data selection section, the number of frame intervals between a pair of RF signal frame data used for generating elastic frame for a current image configuration, and calculates an optimum number of frame intervals of a pair of RF signal frame data to be used for generating elastic frame data for a subsequent image configuration, based on the received number of frame intervals and the statistical characteristic amount from the processing section; and wherein said RF signal frame data selection section is configured to include means, connected to the frame interval optimization means, which determines the number of frame intervals of the pair of RF signal frame data to be used for generating elastic frame data for a subsequent image configuration, based on the optimum number of frame intervals received from the frame interval optimization means.
 9. The ultrasonographic device according to claim 8, wherein the calculation of an optimum number of frame intervals of a pair of RF signal frame data to be used for generating elastic frame data for a subsequent image configuration based on the received number of frame intervals and the statistical characteristic amount from the processing section further includes: means for calculating the optimum number of frame intervals based on the received number of frame intervals and an average value of distortion amounts.
 10. The ultrasonographic device according to claim 1, wherein the statistical characteristic amount is an average value of distortions of the elastic frame data.
 11. A method of generating an elastic image in an ultrasonographic device, comprising the steps of: transmitting and receiving an ultrasonic wave to and from a test subject through an ultrasound probe including an oscillator for generating an ultrasonic wave; controlling a phase of a received ultrasonic wave and generating RF signal frame data; selecting said RF signal frame data; generating elastic frame data indicating a distortion or an elastic modulus based on a pair of RF signal frame data selected; setting an upper limit value and a lower limit value of a gradation range for imaging so that a statistical characteristic amount of said elastic frame data which is generated matches with a center of the gradation range; and generating an elastic image based on said elastic frame data by correlating the gradation range to said upper and lower limit values.
 12. A method according to claim 11, wherein the upper and lower limit values are obtained by the following equations: upper limit value=(average value)+(constant D)×(variance value); and lower limit value=(average value)−(constant E)×(variance value).
 13. The method according to claim 11, wherein the statistical characteristic amount is an average value of distortions of the elastic frame data.
 14. An ultrasonographic device, comprising: an ultrasound probe including an oscillator configured to generate an ultrasonic wave; an ultrasonic wave transmitter/receiver section which is connected to the probe and configured to transmit and receive the ultrasonic wave to and from a test subject; an elastic frame data calculation section configured to generate elastic frame data from the received ultrasonic wave; a processing section configured to set an upper limit value and a lower limit value of a range for imaging based upon a statistical characteristic amount of said elastic frame data generated by said elastic frame data calculation section; and an elastic image generating section configured to generate an elastic image based on said elastic frame data by correlating a gradation range to said upper limit value and said lower limit value; and wherein said statistical characteristic amount is an average value and a variance value of said elastic frame data.
 15. The ultrasonographic device according to claim 14, wherein said processing section is configured to obtain said upper and lower limit values by the following equations: upper limit value=(average value)+(constant D)×(variance value); and lower limit value=(average value)−(constant E)×(variance value).
 16. A method of generating an elastic image of a test subject utilizing an ultrasonographic device, comprising the steps of: generating an ultrasonic wave utilizing an ultrasound probe including an oscillator; transmitting and receiving the ultrasonic wave to and from the test subject; generating elastic frame data from the received ultrasonic wave utilizing an elastic frame data calculation section; setting an upper limit value and a lower limit value of a gradation range for imaging so that a statistical characteristic amount of said elastic frame data generated by the elastic frame data calculation section utilizing a processing section matches with a center of the gradation range; and generating an elastic image based on the elastic frame data by correlating the gradation range to said upper limit value and said lower limit value utilizing an elastic image generating section.
 17. The method according to claim 16, wherein said statistical characteristic amount is an average value and a variance value of said elastic frame data.
 18. The method according to claim 16, wherein processing section is configured to obtain both of said upper and lower limit values by the following equations: upper limit value=(average value)+(constant D)×(variance value); and lower limit value=(average value)−(constant E)×(variance value).
 19. The method according to claim 16, wherein the statistical characteristic amount is an average value of distortions of the elastic frame data. 